[spirv-reader] Refactor bookkeeping for localy defined values
Bug: tint:3
Change-Id: Ibe26b802ae61c6271f8a75e641ac31db36df6000
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/24124
Reviewed-by: dan sinclair <dsinclair@google.com>
diff --git a/src/reader/spirv/function.cc b/src/reader/spirv/function.cc
index 8b89d80..1fe4614 100644
--- a/src/reader/spirv/function.cc
+++ b/src/reader/spirv/function.cc
@@ -409,7 +409,13 @@
BlockInfo::BlockInfo(const spvtools::opt::BasicBlock& bb)
: basic_block(&bb), id(bb.id()) {}
-BlockInfo::~BlockInfo() {}
+BlockInfo::~BlockInfo() = default;
+
+DefInfo::DefInfo(const spvtools::opt::Instruction& def_inst,
+ uint32_t the_block_pos)
+ : inst(def_inst), block_pos(the_block_pos) {}
+
+DefInfo::~DefInfo() = default;
FunctionEmitter::FunctionEmitter(ParserImpl* pi,
const spvtools::opt::Function& function)
@@ -623,7 +629,6 @@
}
// TODO(dneto): register phis
- // TODO(dneto): register SSA values which need to be hoisted
RegisterValuesNeedingNamedOrHoistedDefinition();
if (!EmitFunctionVariables()) {
@@ -2416,7 +2421,8 @@
const spvtools::opt::Instruction& inst,
TypedExpression ast_expr) {
const auto result_id = inst.result_id();
- if (needs_hoisted_def_.count(result_id) != 0) {
+ const auto* def_info = GetDefInfo(result_id);
+ if (def_info && def_info->requires_hoisted_def) {
// Emit an assignment of the expression to the hoisted variable.
AddStatement(std::make_unique<ast::AssignmentStatement>(
std::make_unique<ast::IdentifierExpression>(namer_.Name(result_id)),
@@ -2430,20 +2436,24 @@
const auto result_id = inst.result_id();
// Handle combinatorial instructions.
auto combinatorial_expr = MaybeEmitCombinatorialValue(inst);
+ const auto* def_info = GetDefInfo(result_id);
if (combinatorial_expr.expr != nullptr) {
- if ((needs_hoisted_def_.count(result_id) == 0) &&
- (needs_named_const_def_.count(result_id) == 0) &&
- (def_use_mgr_->NumUses(&inst) == 1)) {
- // If it's used once, and doesn't need a named constant definition,
- // then defer emitting the expression until it's used. Any supporting
- // statements have already been emitted.
- singly_used_values_.insert(
- std::make_pair(result_id, std::move(combinatorial_expr)));
- return success();
+ if (def_info == nullptr) {
+ return Fail() << "internal error: result ID %" << result_id
+ << " is missing a def_info";
}
- // Otherwise, generate a const definition for it now and later use
- // the const's name at the uses of the value.
- return EmitConstDefOrWriteToHoistedVar(inst, std::move(combinatorial_expr));
+ if (def_info->requires_hoisted_def || def_info->requires_named_const_def ||
+ def_info->num_uses != 1) {
+ // Generate a const definition or an assignment to a hoisted definition
+ // now and later use the const or variable name at the uses of this value.
+ return EmitConstDefOrWriteToHoistedVar(inst,
+ std::move(combinatorial_expr));
+ }
+ // It is harmless to defer emitting the expression until it's used.
+ // Any supporting statements have already been emitted.
+ singly_used_values_.insert(
+ std::make_pair(result_id, std::move(combinatorial_expr)));
+ return success();
}
if (failed()) {
return false;
@@ -2906,85 +2916,91 @@
}
void FunctionEmitter::RegisterValuesNeedingNamedOrHoistedDefinition() {
- // Maps a result ID to the block position where it is last used.
- std::unordered_map<uint32_t, uint32_t> id_to_last_use_pos;
- // List of pairs of (result id, block position of the definition).
- std::vector<std::pair<uint32_t, uint32_t>> id_def_pos;
-
+ // Create a DefInfo for each value definition in this function.
for (auto block_id : block_order_) {
const auto* block_info = GetBlockInfo(block_id);
const auto block_pos = block_info->pos;
-
for (const auto& inst : *(block_info->basic_block)) {
const auto result_id = inst.result_id();
- if (result_id != 0) {
- id_def_pos.emplace_back(
- std::pair<uint32_t, uint32_t>{result_id, block_pos});
+ if ((result_id == 0) || inst.opcode() == SpvOpLabel) {
+ continue;
}
- inst.ForEachInId(
- [&id_to_last_use_pos, block_pos](const uint32_t* id_ptr) {
- // If the id is not in the map already, this will create
- // an entry with value 0.
- auto& pos = id_to_last_use_pos[*id_ptr];
- // Update the entry.
- pos = std::max(pos, block_pos);
- });
+ def_info_[result_id] = std::make_unique<DefInfo>(inst, block_pos);
+ }
+ }
- if (inst.opcode() == SpvOpVectorShuffle) {
- // We might access the vector operands multiple times. Make sure they
- // are evaluated only once.
- for (auto index : std::array<uint32_t, 2>{0, 1}) {
- auto id = inst.GetSingleWordInOperand(index);
- if (constant_mgr_->FindDeclaredConstant(id)) {
- // If it's constant, then avoid making a const definition
- // in the wrong place; it would be wrong if it didn't
- // dominate its uses.
- continue;
- }
- // Othewrise, register it.
- needs_named_const_def_.insert(id);
+ // Mark vector operands of OpVectorShuffle as needing a named definition,
+ // but only if they are defined in this function as well.
+ for (auto& id_def_info_pair : def_info_) {
+ const auto& inst = id_def_info_pair.second->inst;
+ if (inst.opcode() == SpvOpVectorShuffle) {
+ // We might access the vector operands multiple times. Make sure they
+ // are evaluated only once.
+ for (auto index : std::array<uint32_t, 2>{0, 1}) {
+ auto id = inst.GetSingleWordInOperand(index);
+ auto* operand_def = GetDefInfo(id);
+ if (operand_def) {
+ operand_def->requires_named_const_def = true;
}
}
}
}
+ // Scan uses of locally defined IDs, to determine the block position
+ // of its last use.
+ for (auto block_id : block_order_) {
+ const auto* block_info = GetBlockInfo(block_id);
+ const auto block_pos = block_info->pos;
+ for (const auto& inst : *(block_info->basic_block)) {
+ // Update the usage span for IDs used by this instruction.
+ inst.ForEachInId([this, block_pos](const uint32_t* id_ptr) {
+ auto* def_info = GetDefInfo(*id_ptr);
+ if (def_info) {
+ def_info->num_uses++;
+ def_info->last_use_pos = std::max(def_info->last_use_pos, block_pos);
+ }
+ });
+ }
+ }
+
// For an ID defined in this function, if it is used in a different construct
// than its definition, then it needs a named constant definition. Otherwise
// we might sink an expensive computation into control flow, and hence change
// performance.
- for (const auto& id_and_pos : id_def_pos) {
- const auto id = id_and_pos.first;
- const auto def_pos = id_and_pos.second;
+ for (auto& id_def_info_pair : def_info_) {
+ const auto def_id = id_def_info_pair.first;
+ auto* def_info = id_def_info_pair.second.get();
+ if (def_info->num_uses == 0) {
+ // There is no need to adjust the location of the declaration.
+ continue;
+ }
+ const auto last_use_pos = def_info->last_use_pos;
- auto last_use_where = id_to_last_use_pos.find(id);
- if (last_use_where != id_to_last_use_pos.end()) {
- const auto last_use_pos = last_use_where->second;
- const auto* const def_in_construct =
- GetBlockInfo(block_order_[def_pos])->construct;
- const auto* const construct_with_last_use =
- GetBlockInfo(block_order_[last_use_pos])->construct;
+ const auto* const def_in_construct =
+ GetBlockInfo(block_order_[def_info->block_pos])->construct;
+ const auto* const construct_with_last_use =
+ GetBlockInfo(block_order_[last_use_pos])->construct;
- // Find the smallest structured construct that encloses the definition
- // and all its uses.
- const auto* enclosing_construct = def_in_construct;
- while (enclosing_construct &&
- !enclosing_construct->ContainsPos(last_use_pos)) {
- enclosing_construct = enclosing_construct->parent;
- }
- // At worst, we go all the way out to the function construct.
- assert(enclosing_construct != nullptr);
+ // Find the smallest structured construct that encloses the definition
+ // and all its uses.
+ const auto* enclosing_construct = def_in_construct;
+ while (enclosing_construct &&
+ !enclosing_construct->ContainsPos(last_use_pos)) {
+ enclosing_construct = enclosing_construct->parent;
+ }
+ // At worst, we go all the way out to the function construct.
+ assert(enclosing_construct != nullptr);
- if (def_in_construct != construct_with_last_use) {
- if (enclosing_construct == def_in_construct) {
- // We can use a plain 'const' definition.
- needs_named_const_def_.insert(id);
- } else {
- // We need to make a hoisted variable definition.
- // TODO(dneto): Handle non-storable types, particularly pointers.
- needs_hoisted_def_.insert(id);
- auto* hoist_to_block = GetBlockInfo(enclosing_construct->begin_id);
- hoist_to_block->hoisted_ids.push_back(id);
- }
+ if (def_in_construct != construct_with_last_use) {
+ if (enclosing_construct == def_in_construct) {
+ // We can use a plain 'const' definition.
+ def_info->requires_named_const_def = true;
+ } else {
+ // We need to make a hoisted variable definition.
+ // TODO(dneto): Handle non-storable types, particularly pointers.
+ def_info->requires_hoisted_def = true;
+ auto* hoist_to_block = GetBlockInfo(enclosing_construct->begin_id);
+ hoist_to_block->hoisted_ids.push_back(def_id);
}
}
}
diff --git a/src/reader/spirv/function.h b/src/reader/spirv/function.h
index 484df30..40e23c2 100644
--- a/src/reader/spirv/function.h
+++ b/src/reader/spirv/function.h
@@ -159,8 +159,8 @@
std::string flow_guard_name = "";
/// The result IDs that this block is responsible for declaring as a
- /// hoisted variable. See the |needs_hoisted_def_| member of
- /// FunctionEmitter for an explanation.
+ /// hoisted variable. See the |requires_hoisted_def| member of
+ /// DefInfo for an explanation.
std::vector<uint32_t> hoisted_ids;
};
@@ -174,6 +174,62 @@
return o;
}
+/// Bookkeeping info for a SPIR-V ID defined in the function.
+/// This will be valid for result IDs for:
+/// - instructions that are not OpLabel, OpVariable, and OpFunctionParameter
+/// - are defined in a basic block visited in the block-order for the function.
+struct DefInfo {
+ /// Constructor.
+ /// @param def_inst the SPIR-V instruction defining the ID
+ /// @param block_pos the position of the basic block where the ID is defined.
+ DefInfo(const spvtools::opt::Instruction& def_inst, uint32_t block_pos);
+ /// Destructor.
+ ~DefInfo();
+
+ /// The SPIR-V instruction that defines the ID.
+ const spvtools::opt::Instruction& inst;
+ /// The position of the block that defines this ID, in the function block
+ /// order. See method |FunctionEmitter::ComputeBlockOrderAndPositions|
+ const uint32_t block_pos = 0;
+
+ /// The number of uses of this ID.
+ uint32_t num_uses = 0;
+
+ /// The block position of the last use of this ID, or 0 if it is not used
+ /// at all. The "last" ordering is determined by the function block order.
+ uint32_t last_use_pos = 0;
+
+ /// True if this ID requires a WGSL 'const' definition, due to context. It
+ /// might get one anyway (so this is *not* an if-and-only-if condition).
+ bool requires_named_const_def = false;
+
+ /// True if this ID must map to a WGSL variable declaration before the
+ /// corresponding position of the ID definition in SPIR-V. This compensates
+ /// for the difference between dominance and scoping. An SSA definition can
+ /// dominate all its uses, but the construct where it is defined does not
+ /// enclose all the uses, and so if it were declared as a WGSL constant
+ /// definition at the point of its SPIR-V definition, then the WGSL name
+ /// would go out of scope too early. Fix that by creating a variable at the
+ /// top of the smallest construct that encloses both the definition and all
+ /// its uses. Then the original SPIR-V definition maps to a WGSL assignment
+ /// to that variable, and each SPIR-V use becomes a WGSL read from the
+ /// variable.
+ /// TODO(dneto): This works for constants of storable type, but not, for
+ /// example, pointers.
+ bool requires_hoisted_def = false;
+};
+
+inline std::ostream& operator<<(std::ostream& o, const DefInfo& di) {
+ o << "DefInfo{"
+ << " inst.result_id: " << di.inst.result_id()
+ << " block_pos: " << di.block_pos << " num_uses: " << di.num_uses
+ << " last_use_pos: " << di.last_use_pos << " requires_named_const_def: "
+ << (di.requires_named_const_def ? "true" : "false")
+ << " requires_hoisted_def: " << (di.requires_hoisted_def ? "true" : "false")
+ << "}";
+ return o;
+}
+
/// A FunctionEmitter emits a SPIR-V function onto a Tint AST module.
class FunctionEmitter {
public:
@@ -288,12 +344,16 @@
/// - When a SPIR-V instruction might use the dynamically computed value
/// only once, but the WGSL code might reference it multiple times.
/// For example, this occurs for the vector operands of OpVectorShuffle.
- /// In this case the definition is added to |needs_named_const_def_|.
+ /// In this case the definition's |requires_named_const_def| property is
+ /// set to true.
/// - When a definition and at least one of its uses are not in the
/// same structured construct.
- /// In this case the definition is added to |needs_named_const_def_|.
+ /// In this case the definition's |requires_named_const_def| property is
+ /// set to true.
/// - When a definition is in a construct that does not enclose all the
- /// uses. In this case the definition is added to |needs_hoisted_def_|.
+ /// uses. In this case the definition's |requires_hoisted_def| property
+ /// is set to true.
+ /// Populates the |def_info_| mapping.
void RegisterValuesNeedingNamedOrHoistedDefinition();
/// Emits declarations of function variables.
@@ -495,8 +555,20 @@
/// @returns the block info for the given ID, if it exists, or nullptr
BlockInfo* GetBlockInfo(uint32_t id) const {
auto where = block_info_.find(id);
- if (where == block_info_.end())
+ if (where == block_info_.end()) {
return nullptr;
+ }
+ return where->second.get();
+ }
+
+ /// Gets the local definition info for a result ID.
+ /// @param id the SPIR-V ID of local definition.
+ /// @returns the definition info for the given ID, if it exists, or nullptr
+ DefInfo* GetDefInfo(uint32_t id) const {
+ auto where = def_info_.find(id);
+ if (where == def_info_.end()) {
+ return nullptr;
+ }
return where->second.get();
}
@@ -622,21 +694,6 @@
std::unordered_set<uint32_t> identifier_values_;
// Mapping from SPIR-V ID that is used at most once, to its AST expression.
std::unordered_map<uint32_t, TypedExpression> singly_used_values_;
- // Set of SPIR-V IDs which should get a named const definition.
- std::unordered_set<uint32_t> needs_named_const_def_;
- // The SPIR-V IDs that must be declared in WGSL before the corresponding
- // location in SPIR-V. This compensates for the difference between dominance
- // and scoping. An SSA definition can dominate all its uses, but the construct
- // where it is defined does not enclose all the uses, and so if it were
- // declared as a WGSL constant definition at the point of its SPIR-V
- // definition, then the WGSL name would go out of scope too early. Fix that by
- // creating a variable at the top of the smallest construct that encloses both
- // the definition and all its uses. Then the original SPIR-V definition maps
- // to a WGSL assignment to that variable, and each SPIR-V use becomes a WGSL
- // read from the variable.
- // TODO(dneto): This works for constants of storable type, but not, for
- // example, pointers.
- std::unordered_set<uint32_t> needs_hoisted_def_;
// The IDs of basic blocks, in reverse structured post-order (RSPO).
// This is the output order for the basic blocks.
@@ -645,6 +702,9 @@
// Mapping from block ID to its bookkeeping info.
std::unordered_map<uint32_t, std::unique_ptr<BlockInfo>> block_info_;
+ // Mapping from a locally-defined result ID to its bookkeeping info.
+ std::unordered_map<uint32_t, std::unique_ptr<DefInfo>> def_info_;
+
// Structured constructs, where enclosing constructs precede their children.
ConstructList constructs_;
};
